Fuel cell control system and method

ABSTRACT

When an electric power generation demand occurs for a fuel cell stack  1 , an electric power stored in a battery  8  is commenced to be supplied to a load (step S 3 ) followed by setting a period (step S 2 ), in which a sensor signal from a fuel cell system  10  is held in a preceding value, in a subtraction timer, and when discrimination is made (step S 5 , step S 6 ) that the fuel cell system  10  is started up and each pressure is stabilized from a sensor signal from the fuel cell system  10 , the electric power generated in the fuel cell stack  1  is commenced to be supplied to the load (step S 8 ) followed by setting the period, in which the sensor signal from the fuel cell system  10  is held in the preceding value, in the subtraction timer (step S 7 ).

TECHNICAL FIELD

The present invention relates to a control system and method of a fuelcell that generates an electric power for driving a drive motor of afuel cell powered vehicle.

BACKGROUND ART

Normally, in order to increase an electric power generating efficiencyof a fuel cell stack in a fuel cell system, there is a need forincreasing an electric power voltage of the fuel cell stack. However, ifan electric power supply formed by the fuel cell stack is turned on oroff under a condition where an output voltage of the fuel cell stack isincreased, in a case where an initial resistance value of a connectionequipment of the fuel cell stack is low, it is probable that a largeelectric current flows through connecting parts.

On the contrary, a fuel cell system described in Japanese PatentProvisional Publication No. 2002-063925 is configured to prevent a highvoltage from being applied to equipments of a direct current electricpower system by providing a shut-off circuit for thereby protectingconnecting equipments of a fuel cell stack.

DISCLOSURE OF THE INVENTION

Further, in a normal fuel cell system, during electric power generationof the fuel cell stack, first, it is necessary to supply fuel gas andoxidizing gas under a state to enable the fuel cell stack to generatethe electric power and, if these gas pressures exceeds given levels,electric power generation is commenced to allow electric current to betaken out from the fuel cell stack.

However, with such a fuel cell system, since a large electric currentflows at the same time that the electric power is taken out from thefuel cell stack, there seems to be a probability in that detectionnoises occur even though a pressure sensor for fuel gas and atemperature sensor do not form equipments of a direct current electricpower system with respect to an electric current system of the fuel cellsystem. Thus, if large noises occur in a sensor signal related to, forinstance, a fuel gas pressure, erroneous discrimination is made that alarge differential pressure is created between fuel gas and oxidizinggas and, further, erroneous discrimination is made that the differentialpressure between fuel gas and oxidizing gas falls in a high value thatinduces an operational inability, providing a probability of resultantinterruption of the fuel cell system per se.

Thus, the present invention has been made in view of the above actualstates and a first aspect of the present invention is a fuel cellcontrol system comprising a fuel cell stack, a fuel cell system takingout an electric power generated by the fuel stack to be supplied to aload, and a control section controlling an electric power generatingoperation of the fuel cell stack based on a sensor signal inputted froma sensor disposed in the fuel cell system, wherein the control sectioncontrols the fuel cell system such that, during startup of the fuel cellsystem, a gas supply pressure of the fuel cell stack in compliance withthe sensor signal inputted from the sensor is discriminated to bestabilized at an electric power generation start pressure of the fuelcell stack, a time duration, involving an electric power taking outstart timing at which an electric power is taken out from the fuel cellstack, is set as a period in which the sensor signal is held in apreceding value and gas supply to the fuel cell stack is commenced basedon the sensor signal held in the preceding value.

A second aspect of the present invention is a fuel cell control systemcomprising a fuel cell stack, a fuel cell system taking out an electricpower generated by the fuel stack to be supplied to a load, and acontrol section controlling an electric power generating operation ofthe fuel cell stack based on a sensor signal inputted from a sensordisposed in the fuel cell system, wherein the control section controlsthe fuel cell system such that, during stop of the fuel cell system, agas supply pressure of the fuel cell stack in compliance with the sensorsignal inputted from the sensor is discriminated to be stabilized, atime duration, involving an electric power taking out start timing atwhich an electric power is taken out from the fuel cell stack, is set asa period in which the sensor signal is held in a preceding value and gassupply to the fuel cell stack is interrupted based on the sensor signalheld in the preceding value.

A third aspect of the present invention is a fuel cell control methodcomprising calculating a gas supply pressure related to a fuel cellstack from a sensor signal inputted from a sensor disposed in a fuelcell system during startup of the fuel cell system, discriminating thatthe gas supply pressure is stabilized at an electric power generationstart pressure of the fuel cell stack, setting a time duration,involving an electric power taking out start timing at which an electricpower is taken out from the fuel cell stack, as a period in which thesensor signal is held in a preceding value, and controlling the fuelcell system so as to begin gas supply to the fuel cell stack based onthe sensor signal held in the preceding value.

A fourth aspect of the present invention is a fuel cell control methodcomprising calculating a gas supply pressure related to a fuel cellstack from a sensor signal inputted from a sensor disposed in a fuelcell system during stop of the fuel cell system, discriminating that thegas supply pressure is stabilized at an electric power generation startpressure of the fuel cell stack, setting a time duration, involving anelectric power taking out start timing at which an electric power istaken out from the fuel cell stack, as a period in which the sensorsignal is held in a preceding value; and controlling the fuel cellsystem so as to stop gas supply to the fuel cell stack based on thesensor signal held in the preceding value.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a structure of a control deviceof a fuel cell system to which the present invention is applied.

FIG. 2 is a block diagram illustrating a concrete structure of the fuelcell system.

FIG. 3 is a flowchart illustrating an operational sequence of anelectric power generation startup control operation to be performed by asystem control section for starting up the fuel cell system to startelectric power generation.

FIG. 4 is a flowchart illustrating an operational sequence of a fuelcell system monitoring control operation to be performed by the systemcontrol section for monitoring a status of the fuel cell system.

FIG. 5 is a flowchart illustrating an operational sequence of anelectric power generation stop control operation to be performed by thesystem control section for stopping the electric power generation of thefuel cell system.

FIGS. 6A to 6G are views illustrating an effect of the control device ofthe fuel cell system to which the present invention is applied, withFIG. 6A showing operation of a battery J/B, FIG. 6B showing operation ofa stack J/B, FIG. 6C showing a sensor signal produced by a fuel pressuresensor, FIG. 6D showing a sensor signal produced by a coolant watersensor, FIG. 6E showing a period in which a preceding value is held bythe system control section, FIG. 6F representing a time change of adifferential pressure between a fuel pressure gas and a coolant waterpressure detected by the system control section and FIG. 6G representinga time change of the differential pressure between the fuel pressure gasand the coolant water pressure detected by a system control section of acomparison.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment according to the present invention isdescribed with reference to the drawings.

The present invention is applied to a control device 100 of a fuel cellsystem structured as shown in FIG. 1. The control system 100 of the fuelcell system is installed, for instance, in a fuel cell powered vehiclehaving a fuel cell stack 1 as a drive source. The fuel cell stack 1serves to achieve electrochemical reaction between fuel gas, such ashydrogen or the like, and oxidizing gas containing oxygen by means ofelectrolyte, thereby directly taking out electric power from electrodes.

In the control system 100 of such a fuel cell system, the fuel cellstack 1 is connected to a stack J/B (junction box) 3 and an electricpower control section 4 with high voltage line 2. An electric poweroutput voltage generated at the fuel cell stack 1 is supplied to thestack J/B 3 whereupon the output voltage is regulated by the electricpower control section 4 and supplied to a drive motor 5 and a batteryJ/B 6. By so doing, the drive motor 5 produces an output torque fordriving the fuel cell powered vehicle in dependence on control of amotor controller 7. In the meantime, the output voltage supplied to thebattery J/B 6 is supplied to and stored in a battery (secondary battery)8.

Further, the electric power stored in the battery 8 is discharged inaccordance with control of a battery controller 9, with dischargedelectric power being supplied to the drive motor 5 via the battery J/B6.

Furthermore, the control system 100 of the fuel cell system is comprisedof a fuel cell system 10, permitting the fuel cell stack 1 to performelectric power generation, which is operated in accordance with controlof a system control section 11. The system control section 11 drivinglycontrols the fuel cell system 10 depending on a driving demand of thedrive motor 5 from an external source to initiate or interrupt electricpower generation of the fuel cell stack 1 for controlling the electricpower to be generated by the fuel cell stack 1. When this takes place,the system control section 11 is applied with sensor signals fromvarious sensors, described later, which are located in the fuel cellsystem 10, and controls the fuel cell system 10.

Moreover, the system control section 11 controls the electric powercontrol section 4 to allow the electric power, delivered from the stackJ/B 3, to be regulated and to be supplied to the battery J/B 6 and thedrive motor 5 and controls the battery controller 9 for controllingcharging and discharging of the battery 8, while also controlling themotor controller 7 to control a drive torque of the drive motor 5.

In the control device 100 of the fuel cell system, although a detail isdescribed below, the system control section 11 executes the following:

(1) electric power generation startup control operation for starting upthe fuel cell stack 1 to initiate electric power generation;

(2) fuel cell system monitoring control operation for monitoringoperation of the fuel cell system 10; and

(3) electric power generation stop control operation for stopping thefuel cell stack 1 to terminate electric power generation of the fuelcell stack 1.

[Concrete Structure of Fuel Cell System 10]

Now, a concrete structure of the fuel cell system 10 is described withreference to FIG. 2.

The fuel cell stack 1 includes a fuel electrode 1 a to which fuel gas issupplied and an air electrode 1 b to which air is supplied, with thefuel electrode 1 a and the air electrode 1 b being joined to one anothervia a solid polymer film where respective ions transfer by means ofmedium composed of moisture to be brought into contact with one anotherto generate electric power. Also, the fuel cell stack 1 is internallyequipped with a coolant water conduit for appropriately maintaining afuel cell temperature.

Connected to such a fuel cell stack 1 via a hydrogen delivery pipe are afuel storage tank 21, a fuel gas pressure control valve 22, an ejectorrecirculation unit 23 and a condensed water recovery unit 24, therebysupplying hydrogen to the fuel electrode 1 a as fuel gas.

Fuel gas is compressed in the fuel storage tank 21 to remain under ahigh pressure and is reduced in pressure by the fuel gas pressurecontrol valve 22 to be supplied to the ejector recirculation unit 23.Also, the present embodiment has been shown in conjunction with a casewhere the fuel storage tank 21 and the fuel pressure control valve 22are in direct communication with one another, in addition, another valvefor reducing pressure may be located in a midway between the fuelstorage tank 21 and the fuel gas pressure control valve 22.

Fuel gas passing through the fuel gas pressure control valve 22 issupplied to the ejector recirculation unit 23 through a recirculationdelivery pipe and mixed with fuel gas that passes through the fuelelectrode 1 a and supplied through a condensed water recovery unit 25,whereupon mixed fuel gas is delivered to the condensed water recoveryunit 24 and supplied to the fuel electrode 1 a. When this takes place,the condensed water recovery units 24, serve to condense steam through aradiation heat cooling effect resulting from delivery pipes extendingthrough the fuel cell stack 1 from the ejector recirculation unit 23 toform moisture that is separated from fuel gas, with resulting fuel gasbeing supplied to the fuel cell stack 1 and the ejector recirculationunit 23.

Further, in a case where the electric power generation demand for thefuel cell stack 1 rapidly drops or the operation of the fuel cell stack1 is interrupted, fuel gas which is not consumed by the fuel cell stack1 is passed through a fuel gas exhaust valve 26, located downstream of afuel gas stream of the fuel cell stack 1 and is, for instance, combustedin a hydrogen combustor and subsequently discharged to the outside.Also, although there are many probabilities where, in normal practice,the fuel gas exhaust valve 26 may include an ON/OFF valve to provide anease of control, it may include a flow rate and pressure control valvewhose opening degree is controllable.

Here, the system control section 11 reads in a sensor signal (indicatedby an arrow L1) delivered from a fuel pressure sensor 29 disposed on thefuel gas delivery pipe between the condensed water recovery unit 24 andthe fuel electrode 1 a such that the fuel gas pressure supplied to thefuel electrode 1 a is detected to control an actuator 27 which opens orcloses the fuel gas pressure control valve 22 (as indicated by an arrowL2). By so doing, the flow rate and pressure of fuel gas to be suppliedto the fuel electrode 1 a are regulated and, additionally, an actuator28 for opening and closing the fuel gas exhaust valve 26 is drivinglycontrolled (as shown by an arrow L3).

In the meantime, air is taken out from the atmosphere by a compressor 30and compressed to be fed into an air delivery pipe. Here, since aircompressed by the compressor 30 is raised at a high temperature, for thepurpose of permitting reaction to take place in the fuel cell stack 1 ata high efficiency, air is cooled by an air cooler 31 mounted at an airinlet of the fuel cell stack 1 and supplied to the air electrode 1 b.And, since air with oxygen constituent being consumed at the airelectrode 1 b of the fuel cell stack 1 while containing residual oxygencontains moisture resulting from reaction in the fuel cell stack 1,moisture is recovered in a water recovery unit 32 and, thereafter, airis expelled to the atmosphere through an air pressure regulator valve33. Also, connected to an air exhaust side of the air electrode 1 b isan air purge valve 34 that is rendered opened during an air purge mode.

Here, the system control section 11 drivingly controls the compressor 30to regulate the air flow rate (as shown in an arrow L4) and reads in asensor signal (as shown in an arrow L5) delivered from an air pressuresensor 37 disposed in an air delivery pipe between the air cooler 31 andthe air electrode 1 b to detect the air pressure supplied to the airelectrode 1 b so as to control an actuator 35 (as shown by an arrow L6)for opening and closing the air pressure regulator valve 33 such thatthe air pressure is regulated to allow the air pressure to be equalizedwith the fuel gas pressure. When this occurs, the system control section11 controls the actuator 35 such that, when intended to increase the airpressure, the air pressure regulator valve 33 is operated in a closingdirection. Also, the system control section 11 drivingly controls anactuator 36 (as shown by an arrow L7) such that, during a purge mode ofthe fuel electrode 1 b, the air purge valve 34 is operated in an openingdirection.

The fuel cell system 10 employs ethylene glycol with high boilingtemperature as coolant water of the fuel cell stack 1. This coolantwater is drawn by a pump 38 to be fed from a reservoir tank 39 into acoolant water circulation passage and fed into the fuel cell stack 1 viaa temperature regulator 40 that operates in combination with a radiatorand a fan to maintain the temperature at a constant level. By so doing,the temperature of the fuel cell stack 1 is regulated. Coolant waterpassage through a coolant water delivery pipe in the fuel cell stack 1is heated by electric power generation of the fuel cell stack 1 andaccumulated in the reservoir tank 39 prior to being circulated to thepump 38. This provides functions such as absorption of rapid pressurevariation such as water hummer or an accumulator for the pump flow rate.

Further, disposed in the close proximity to the coolant inlet of thefuel cell stack 1 in the coolant water circulation passage are a coolantwater pressure sensor 41 that detects a coolant water pressure and acoolant water temperature sensor 42 that detects a coolant watertemperature. Also, although the present embodiment has been shown withreference to a case where the coolant water pressure sensor 41 and thecoolant water temperature sensor 42 are disposed at the coolant inlet ofthe fuel cell stack 1, the present embodiment is not restricted theretoand these may be located at a coolant water outlet of the fuel cellstack 1.

Here, the system control section 11 reads in a sensor signal deliveredfrom the coolant water pressure sensor 41 (as shown by an arrow L8) suchthat the pressure of coolant water supplied to the fuel cell stack 1 isdetected to control the discharge flow rate of the pump 38 (as shown byan arrow L9) in dependence on the electric power output of the fuel cellstack 1. Also, other control technique for the coolant water pressuremay include an orifice valve located in the coolant water circulationpassage through which pressure control of coolant water is performed.

[Control Operation by System Control Section]

Next, various control operations to be performed by the system controlsection 11 of the control device 100 of the fuel cell system of thestructure previously mentioned are described.

(1) Electric Power Generation Startup Control Operation

First, an operational sequence of electric power generation startupcontrol operation of the system control section 11 for starting up thefuel cell stack 1 to initiate electric power generation is describedwith reference to a flowchart of FIG. 3. The electric power generationstartup control operation is executed by the system control section 11in synchronism with an internal timer of, for instance, a CPU (CentralProcessing Unit) equally divided time durations each for, for example,10 msec.

For instance, if an electric power generation demand for the fuel cellstack 1 is inputted into the system control section 11 from outside,first in step S1, discrimination is made to see whether insulationresistance of an electric power system is extremely large todiscriminate as to whether electric shock or short circuiting is apt totake place when the power supply of the electric power system is turnedon. If it is discriminated that no electric shock or short circuitingoccur when insulation resistance of a high voltage line 2 exceeds agiven value and the electric power source is turned on, operationproceeds to step S2.

In step S2, prior to turning on the power supply, composed of thebattery 8, by means of the battery J/B 6, a subtraction timer valueTIM_chk1 for holding a preceding value of a sensor signal valuedelivered from the fuel supply system 10 is set to an initial valueTIM_init1 (for instance, 10) to begin holding of the preceding values ofrespective sensor signal values (indicated by arrows L1, L2, L3 in FIG.2) delivered from the fuel pressure sensor 29, the air pressure sensor37 and the coolant water pressure sensor 41, allowing operation toproceed to step S3.

Here, the initial value TIM_init1 is set to have a time durationinvolving a startup timing (start time) at which electric power is takenout from the battery 8 in step S3 described later. In particular, theinitial value TIM_init1 is set to have a period during which it isprobable for noises to occur in the sensor signal when the electricpower is taken out from the battery 8 and have a value that reaches zeroat a time before various sensor signals are detected in step S6described below.

In step S3, the battery controller 9 is controlled by the system controlsection 11 to turn on the battery J/B 6 and, in step S4, discriminationis made to see whether the voltage of the high voltage line 2 of theelectric power system reaches a given range. If the system controlsection 11 discriminates that the electric power system voltage of thehigh voltage line 2 reaches the given range, operation proceeds to stepS5. This given range means a range excluding a high voltage occurringwhen the electric power stored in the battery 8 begins to be supplied tothe high voltage line 2 and is set to a range in which the voltageapplied to the high voltage line 2 is stabilized.

In preparation for the following electric power generation startup ofthe fuel cell stack 1 in step S5, the system control section 11 startsup various parts forming the fuel cell system 10 and operation proceedsto step S6. In particular, the system control section 11 starts upperipheral units of the fuel cell stack 1, such as the compressor 30 forsupplying air, the ejector circulation unit 23 for supplying fuel gas,the pump 38 for circulating coolant water and the temperature regulator40.

In step S6, the system control section 11 is applied with the sensorsignals (the arrows L1, L5, L8) from the fuel pressure sensor 29, theair pressure sensor 37 and the coolant water pressure sensor 41 anddiscriminates to see whether the hydrogen pressure, the air pressure andthe coolant water pressure remain at respective stabilized levelssufficient for starting electric power generation of the fuel cell stack1. If the system control section 11 discriminates that fluctuations inthe respective sensor signals, resulting from the start at which theelectric power is taken out from the battery 8, converge and therespective pressures stand stabilized, then, operation proceeds to stepS7.

In step S7, for the purpose of setting the subtraction timer differentfrom that of step S2, a subtraction timer value TIM_chk2 for holding thepreceding value of the sensor signal value is set to an initial valueTIM_init2 (for instance, 10) to begin holding of the preceding values ofrespective sensor signal values (indicated by arrows L1, L2, L3 in FIG.2) delivered from the fuel pressure sensor 29, the air pressure sensor37 and the coolant water pressure sensor 41, allowing operation toproceed to step S8, and controlling the stack J/B 3 and the electricpower control section 4 begins taking out the electric power from thefuel cell stack 1 while terminating operation.

Here, the initial value TIM_init2 is set to have a time durationinvolving a startup timing (start time) at which electric power is takenout from the fuel cell stack 1 in step S8 described later. Inparticular, the initial value TIM_init2 is set to have a period duringwhich it is probable for noises to occur in the sensor signal when theelectric power is taken out from the fuel cell stack 1 and have a valuethat reaches zero at a time before various sensor signals are detectedin step S6 described below.

(2) Fuel Cell System Monitoring Control Operation

Next, an operational sequence of the system control section 11 formonitoring control operation of the fuel cell system for monitoring astatus of the fuel cell system 10 after the fuel cell system 10 has beenstarted up upon execution of the above-described fuel cell systemmonitoring control operation is described with reference to a flowchartof FIG. 4.

During fuel cell system monitoring control operation, independently ofelectric power generation startup control operation, an abnormality ismonitored at the same time that the fuel cell system 10 has been staredup.

First in step S11, upon discrimination of the system control section 11to see whether the subtraction timer value TIM_chk1, that is set in stepS2, and the subtraction timer value TIM_chk2 set in step S7 do not fallto zero, the system control section 11 discriminates to see whether thesensor signal value remains in the period in which the preceding valueis held.

If the system control section 11 discriminates that the sensor signalvalue does not fall in the period in which the preceding value is held,then, operation proceeds to step S12 and is applied with the sensorsignals (the arrows L1, L5, L8) delivered from the fuel pressure sensor29, the air pressure sensor 37 and the coolant water pressure 41whereupon operation proceeds to step S14.

In the meantime, if the system control section 11 discriminates that thesensor signal value falls in the period in which the preceding value isheld, operation proceeds to step S13 and respective subtraction timervalues, which are set in step S2 and step S7, are subtracted whileproceeding operation to step S14. That is, the system control section 11performs operation of step S14 while holding the sensor signals in therespective preceding values.

In step S14, using the respective sensor signal values, the systemcontrol section 11 discriminates to see whether a differential pressurebetween the fuel gas pressure and the air pressure, a differentialpressure between the air pressure and the coolant water pressure and adifferential pressure between the coolant water pressure and the fuelgas pressure fall in given values and, if it is discriminated that therespective differential pressures fall in the respective given values,then, operation is terminated. Here, the given values to be comparedwith the respective differential pressures are set to differentialpressure values, during system designs, which have probabilities tocause the fuel cell stack 1 to be damaged due to the respective pressuredifferences.

In the meantime, if the system control section 11 discriminates thateither one of the differential pressures does not fall to the givenvalue, the system control section 11 judges that either one of thepressure differences has an abnormal value and there is a probability ofoccurrence of damage in the fuel cell stack 1, and interrupts operationsof various parts forming the fuel cell system 10 to stop the supply offuel while terminating operation.

(3) Electric Power Generation Stop Control Operation

Next, an operational sequence of the system control section 11 forimplementing electric power generation stop control operation to stopelectric power generation of the fuel cell stack 1 is described withreference to a flowchart of FIG. 5.

For instance, if a request for stop of electric power generation of thefuel cell stack 1 is inputted to the system control section 11 fromoutside, first in step S21, the system control section 11 is appliedwith the respective sensor signals (indicated by the arrows L1, L5, L8)to discriminate whether the fuel gas pressure, the air pressure and thecoolant water pressure remain in given ranges and, if it isdiscriminated that these remain in the given ranges, operation proceedsto step S22.

In step S22, the system control section 11 sets the subtraction timervalue TIM_chk2, related to the fuel cell stack 1, to the initial valueTIM_init2 to start subtraction of the subtraction timer value whileholding the sensor signal values, and operation proceeds to step S23.

Here, the initial value TIM_init2 is set to have a time period involvinga stop timing (stop time) for stopping the electric power from beingtaken out of the fuel cell stack 1 in step S23. In particular, theinitial value TIM_init2 is set to have a period that has a probabilityof noises occurring in the sensor signal due to stop of the electricpower being taken out from the fuel cell stack 1.

In step S23, the stack J/B 3 is controlled by the system control section11 to cut out the voltage to be supplied to the electric power controlsection 4 from the fuel cell stack 1 and operation proceeds to step S24,interrupting operations of various parts forming the fuel cell stack 10while proceeding operation to step S25.

In step S25, the system control section 11 discriminates to see whetherthe electric power generation of the fuel cell stack 1 in step S24 tocause the electric power system voltage in the high voltage line 2 todrop to allow the electric power system voltage in the high voltage line2 to fall in a given range. If the system control section 11discriminates that the electric power system voltage in the high voltageline 2 falls in the given range, operation proceeds to step S26.

In step S26, the subtraction timer value TIM_chk1, related to thebattery 8, is set to the initial value TIM_init1 by the system controlsection 11 to begin subtraction of the subtraction timer value to allowoperation to proceed to step S27, thereby blocking the voltage frombeing supplied from the battery to the drive motor 5 via the battery J/B6 and terminating operation.

Here, the initial value TIM_init1 to be determined for the subtractiontimer value TIM_chk1 is set to have a time duration involving a stoptiming (stop time) to interrupt the electric power being taken out fromthe battery in step S27. In particular, the initial value TIM_init1 isset to have a period that has a probability of noises occurring in thesensor signal due to stop of the electric power being taken out from thebattery 8.

Next, a control effect provided by the system control section 11 forperforming such control operation is described with reference to FIGS.6A to 6G.

According to the control device 100 of the fuel cell system equippedwith the system control section 11 which performs such controloperation, if the electric power begins to be taken out from the battery8 at a time T1 (see FIG. 6A), noises occur in the sensor signal (thearrow L1) delivered from the fuel pressure sensor 29 and the sensorsignal (the arrow L8) delivered from the coolant water pressure sensor41 (see FIGS. 6C, 6D). This is because of the fact that noises of theelectric power system connecting the battery 8 and the drive motor 5affect on control lines which connect the system control section 11 andthe fuel cell system 10.

When this takes place, although, in the fuel cell system 10, there is nooccurrence in rapid fluctuation in the differential pressure between thefuel gas pressure and the coolant water pressure, the system controlsection 11 comes to be applied with the sensor signals with profilesshown in FIGS. 6C and 6D.

On the contrary, since the presently filed embodiment permits the sensorsignals to be held in the respective preceding values in step S2 priorto electrical connection between the battery 8 and the drive motor 5 instep S3, as shown in FIG. 3, during the electric power generationstartup control operation, even if noises occur in the sensor signal instep S3, the resulting signal value is not effective to control the fuelcell system 10. That is, in the system control section 11, as shown inFIG. 6F, since the sensor signal value appearing in step S2 is used,control of the fuel cell system 10 is performed under a condition whereno differential pressure exists between the fuel gas pressure and thecoolant water pressure.

In a case where, as comparison with respect to the presently filedembodiment, if the sensor signal, associated with electrical connectionbetween the battery 8 and the drive motor 5, is used as it is, as shownin FIG. 6G, there is a probability in which the system control section11 makes an erroneous discrimination that the differential pressurebetween the fuel gas pressure and the coolant water pressure becomeslarge to stop operation of the fuel cell system 10 and, further, stopsthe start for electric power generation of the fuel cell stack 1.

Namely, since the presence of excessively increasing pressure differencebetween fuel gas and coolant water to be supplied to the fuel cell stack1 leads the fuel cell stack 1 to be damaged, the system control section11 monitors the differential pressures at all times and stops the fuelcell system 10 when detecting that the differential pressure increasesto an extent causing the fuel cell stack 1 to be damaged.

Further, even if subsequent to electrical connection between the battery8 and the drive motor 5, the fuel cell stack 1 generates electric powerat time T2 and the fuel cell stack 1 and the drive motor 5 areelectrically connected (see FIG. 6B), the presently filed embodimentcontrols the fuel cell system 10 under a condition with no recognitionof the differential pressure, whereas comparison has a probability inwhich the differential pressure is recognized and operation of the fuelcell system 10 is stopped.

Consequently, according to the control device 100 of the fuel cellsystem of the presently filed embodiment, in a case where the fuel cellstack 1 and the battery 8, and the drive motor 5 are electricallyconnected to allow the electric power system power source to be turnedon during the electric power generation startup control operation, evenif noises occur in the sensor signal vales to be supplied from the fuelcell system 10 to the system control section 11, it is possible toprevent the fuel cell system 10 from making erroneous discrimination inthat the differential pressure between fuel gas and coolant waterbecomes large.

Furthermore, since the control device 100 of such a fuel cell systemperforms the fuel cell system monitoring control operation under thecondition where the sensor signals are held in the preceding values forthe period during which the subtraction timer value reaches zero afterthe electric power system has been turned on, it is possible to precludeerroneous discrimination in that a large pressure difference occurs inthe period when noises occur in the sensor signals due to power supplyturning-on of the electric power system.

Moreover, according to the control device 100 of the fuel cell system,even if noises occur in the sensor signal values when interruptingoperation of the electric power system during electric power generationstartup control operation, it is possible to preclude the fuel cellsystem 10 from making erroneous discrimination in that the differentialpressure between fuel gas and coolant water is large.

In addition, according to the control device 100 of the fuel cellsystem, since discrimination is made that, prior to holding therespective sensor signals in the preceding values, the fuel gaspressure, the air pressure and the coolant water pressure are adequatelystabilized in a state necessary for starting the electric powergeneration of the fuel cell stack 1, it is possible to accuratelyperform control of a status where pressures assume values for the startof the electric power generation using the sensor signals delivered fromthe respective sensors, thereby reliably precluding the fuel cell stack1 from being damaged due to an increase in each pressure differenceduring such a period.

Also, the above-described embodiment forms an example of the presentinvention. For this reason, the present invention is not limited to thepresently filed embodiment set forth above and, of course, when theinvention is embodied in other forms, various modifications may be madein compliance with designs without departing from the technical conceptof the present invention.

The entire content of Japanese Application No. P2002-178975 with afiling date of Jun. 19, 2002 is herein incorporated by reference.

Although the present disclosure has been described above by reference tocertain embodiments of the invention, the invention is not limited tothe embodiments described above and modifications will occur to thoseskilled in the art, in light of the teachings. The scope of theinvention is defined with reference to the following claims.

INDUSTRIAL APPLICABILITY

According to the present invention, since during a start for taking outelectric power from a fuel cell stack 1 and a stop of a fuel cellsystem, sensor signals are held in preceding values under a conditionwhere gas supply pressures are stabilized, it is possible to preventerroneous diagnosis from being caused by noises even in occurrence ofnoises in the sensor signals during the start and stop of the electricpower being taken out from the fuel cell stack.

1. A fuel cell control system comprising: a fuel cell stack; a fuel cell system for taking out an electric power generated by the fuel cell stack to be supplied to a load; and a control section for controlling an electric power generating operation of the fuel cell stack based on a sensor signal inputted from a sensor disposed in the fuel cell system, wherein the control section controls the fuel cell system such that, during startup of the fuel cell system, a gas supply pressure of the fuel cell stack in compliance with the sensor signal inputted from the sensor is discriminated to be stabilized at an electric power generation start pressure of the fuel cell stack, a time duration, involving an electric power taking out start timing at which the electric power is taken out from the fuel cell stack, is set as a period in which the sensor signal is held at a preceding value and gas supply to the fuel cell stack is commenced based on the sensor signal held at the preceding value.
 2. The fuel cell control system according to claim 1, wherein the control section controls the fuel cell system so as to begin gas supply to the fuel cell stack after an elapse of a given time interval from a start of taking out electric power stored in a secondary battery.
 3. A fuel cell control system comprising: a fuel cell stack; a fuel cell system for taking out an electric power generated by the fuel cell stack to be supplied to a load; and a control section for controlling an electric power generating operation of the fuel cell stack based on a sensor signal inputted from a sensor disposed in the fuel cell system, wherein the control section controls the fuel cell system such that, during stop of the fuel cell system, a gas supply pressure of the fuel cell stack in compliance with the sensor signal inputted from the sensor is discriminated to be stabilized, a time duration, involving an electric power taking out start timing at which the electric power is taken out from the fuel cell stack, is set as a period in which the sensor signal is held at a preceding value and gas supply to the fuel cell stack is interrupted based on the sensor signal held at the preceding value.
 4. A fuel cell control system comprising: a fuel cell stack; a fuel cell system for taking out an electric power from the fuel cell stack to be supplied to a load; and control means for controlling an electric power generating operation of the fuel cell stack based on a sensor signal inputted from a sensor disposed in the fuel cell system, wherein the control means controls the fuel cell system such that, during startup of the fuel cell system, a gas supply pressure of the fuel cell stack in compliance with the sensor signal inputted from the sensor is discriminated to be stabilized at an electric power generation start pressure of the fuel cell stack, a time duration, involving an electric power taking out start timing at which the electric power is taken out from the fuel cell stack, is set as a period in which the sensor signal is held at a preceding value and gas supply to the fuel cell stack is commenced based on the sensor signal held at the preceding value.
 5. A fuel cell control system comprising: a fuel cell stack; a fuel cell system for taking out an electric power generated by the fuel cell stack to be supplied to a load; and control means for controlling an electric power generating operation of the fuel cell stack based on a sensor signal inputted from a sensor disposed in the fuel cell system, wherein the control means controls the fuel cell system such that, during stop of the fuel cell system, a gas supply pressure of the fuel cell stack in compliance with the sensor signal inputted from the sensor is discriminated to be stabilized, a time duration, involving an electric power taking out start timing at which the electric power is taken out from the fuel cell stack, is set as a period in which the sensor signal is held at a preceding value and gas supply to the fuel cell stack is interrupted based on the sensor signal held at the preceding value.
 6. A fuel cell control method comprising: calculating a gas supply pressure related to a fuel cell stack from a sensor signal inputted from a sensor disposed in a fuel cell system during startup of the fuel cell system; discriminating that the gas supply pressure is stabilized at an electric power generation start pressure of the fuel cell stack; setting a time duration, involving an electric power taking out start timing at which an electric power is taken out from the fuel cell stack, as a period in which the sensor signal is held at a preceding value; and controlling the fuel cell system so as to begin gas supply to the fuel cell stack based on the sensor signal held at the preceding value.
 7. A fuel cell control method comprising: calculating a gas supply pressure related to a fuel cell stack from a sensor signal inputted from a sensor disposed in a fuel cell system during stop of the fuel cell system; discriminating that the gas supply pressure is stabilized at an electric power generation start pressure of the fuel cell stack; setting a time duration, involving an electric power taking out start timing at which an electric power is taken out from the fuel cell stack, as a period in which the sensor signal is held at a preceding value; and controlling the fuel cell system so as to stop gas supply to the fuel cell stack based on the sensor signal held at the preceding value.
 8. The fuel cell control system according to claim 1, wherein the preceding value is a previous measurement inputted from the sensor.
 9. The fuel cell control system according to claim 3, wherein the preceding value is a previous measurement inputted from the sensor.
 10. The fuel cell control system according to claim 4, wherein the preceding value is a previous measurement inputted from the sensor.
 11. The fuel cell control system according to claim 5, wherein the preceding value is a previous measurement inputted from the sensor.
 12. The fuel cell control method according to claim 6, wherein the preceding value is a previous measurement inputted from the sensor.
 13. The fuel cell control method according to claim 7, wherein the preceding value is a previous measurement inputted from the sensor. 